Yet another alternator problem...

Sorry guys, I realise that alternator probs aren't the most exciting topic, but this one is beating me. Basically, it's a Defender 90 that has been re-engined a while ago (previous owner) with an Isuzu 2.8 diesel. When I turn the ignitin key the battery light doesn't light, when I start the engine the battery light doesn't come on and the battery gauge indicates low charge. After about 10 minutes driving the battery light starts to flicker and then stays on, then, a minute or two later it goes out and the battery gauge shoots up to show a normal charge rate and all is well. When we had the really cold wet weather a week or so ago it failed to start charging at all, now, with slightly better weather the pattern I've described happens almost every time. Could this be a poor connection somewhere or is this more like a failing alternator? I'm not sure where to start testing with tis, so any pointers are really appreciated.

Ta muchly!!

Cheers,

Steve

alternator should have an 12v ignition feed via light in dash to ind terminal,could be poor contact from feed to light ,light to alt,if you haqve a good 12v ignition feed you will have alt issue

Loose belt??